Data in the real world are often found in the form of graphs: a mathematical structure where pairs of objects are linked by a relation. For example, a pair of objects could be “Peter” and “UK”, these two objects are linked by a relation that could define “lives in” or “was born in” etc.
Some examples of such graphical data structures include social networks, gene expression networks, and knowledge graphs. Even domains where data are not intuitively seen as graph-structured can sometimes be represented as graphs.